Magnetic order in pyrochlore iridate Nd$_2$Ir$_2$O$_7$ probed by muon spin relaxation

TL;DR

This study uses muon-spin relaxation to reveal the magnetic ordering of Ir and Nd moments in Nd$_2$Ir$_2$O$_7$, showing a close link between metal-insulator transition and magnetic order driven by strong spin-orbit coupling.

Contribution

It provides experimental evidence of magnetic ordering in Nd$_2$Ir$_2$O$_7$ and highlights the role of spin-orbit coupling in its metal-insulator transition and magnetic properties.

Findings

Detection of long-range magnetic order of Ir$^{4+}$ moments below 33 K.

Observation of Nd$^{3+}$ moments ordering below 9 K.

Correlation between metal-insulator transition and magnetic ordering.

Abstract

Muon-spin relaxation results on the pyrochlore iridate Nd$_2$Ir$_2$O$_7$ are reported. Spontaneous coherent muon-spin precession below the metal-insulator transition (MIT) temperature of about 33 K is observed, indicating the appearance of a long-ranged magnetic ordering of Ir$^{4+}$ moments. With further decrease in temperature, the internal field at the muon site increases again below about 9 K. The second increase of internal field suggests the ordering of Nd$^{3+}$ moments, which is consistent with a previous neutron experiment. Our results suggest that the MIT and magnetic ordering of Ir$^{4+}$ moments have a close relationship and that the large spin-orbit coupling of Ir 5\textit{d} electrons plays a key role for both MIT and the mechanism of the magnetic ordering in pyrochlore iridates in the insulting ground state.